Lost for over four decades, a newly rediscovered filmed interview with the original star of the BBC's Doctor Who series is set to shed new light on the early years of the show. William Hartnell played the first Doctor from the programme's inception in 1963 through to the start of its fourth season in 1966. In those days, the show regularly had up to 12 million viewers but for years it was believed that not a single TV interview with Hartnell, who died in 1975, had survived.

Now, as the programme's 50th anniversary approaches, candid film of the actor has finally come to light in a local news archive in Bristol.

The interview was filmed for the BBC regional news programme, Points West, and broadcast on 17 January 1967, mere months after an enforced retirement from Doctor Who because of ill health. It was shot in Hartnell's dressing room at the Gaumont Theatre in Taunton, where the actor was appearing in the panto Puss in Boots.

The three-minute-long black-and-white film was actually discovered in 2009 by researcher Richard Bignell, working on behalf of BBC DVD. "While I was over at the [BBC] Written Archives [Centre], doing some stuff for the DVDs, I thought it would be worth going through the programme logs for regional news programmes," explains Bignell. "So, I had a look through for the four weeks [that Hartnell toured with Puss in Boots] and there were two interviews. There was one for Look East, for the first week of the pantomime at Ipswich and one for Points West from the last week when he was at Taunton … I got in contact with the Look East archive and found that their stuff didn't exist anymore… So, that one's definitely gone. But, I dropped the Bristol library an email, and about 20 minutes later, they got back to me with an email: 'Yes, we've still got it. I've got the can of film sitting on my desk here. What would you like me to do with it?'"

The film was transferred to a digital format at the BBC's Television Centre in the summer of 2011. However, it wasn't until this year that a suitable window arose for the material to be released. It will appear on November's BBC DVD release of The Tenth Planet – Hartnell's final Doctor Who story. "It's been quite a difficult thing not to say anything about it," says Bignell.

The interview was conducted by the director, Roger Mills, who, in 1967 was reporting for Points West. Mills recalls: "I wasn't really a reporter – I was more of a behind-the-camera man – but down in the regions you do everything."

"It's a fascinating insight into Hartnell as a person," says Bignell of the newly recovered film. "You get to appreciate that Hartnell was very much just playing a character. Just like [Patrick] Troughton … Because we're very used to [Hartnell's] very fluffy bumbly first Doctor character, I think that there's a tendency to think that perhaps that's what Bill was like – especially when you hear all the stories about how he fluffed his lines etc. But on this, he's quite lucid and quite clear and quite well-spoken."

Hartnell played the Doctor as an impossibly elderly man, with long white hair and a habit of forgetting people's names. However, in reality, the actor was just 55 when he was cast, with his own short greying hair covered by a long white wig. In fact, when new Doctor Peter Capaldi begins shooting the next series of Doctor Who in the new year, he will in fact be a little older than Hartnell was when he first started on the show.

The interview is an occasionally terse one. "I do remember that he didn't want to be interviewed. He was extremely grumpy," recalls Mills. "He really wanted us out as quickly as possible …I don't think he liked the press very much."

"His reputation for being a grumpy old so-and-so really does come over in this particular interview," adds Bignell. "The interviewer says to him at one point, something along the lines of: 'Is pantomime something you'd like to continue doing in the future?' And he sort of goes: 'Ooh, no, no, no, no, no.' So, he says: 'Oh, why not?' And he says: 'Well, I'm a legitimate actor. Pantomime is for the sort of person who is used to variety and going on the front of the stage, but I'm a legitimate actor. I do legitimate things.' He very much comes over with that sort of gruff manner. In fact, towards the end of the interview, the actual interviewer says to him: 'You're actually quite a grumpy man. Why do you think that people like the Doctor so much?'"

"I was someone who didn't hold back," explains Mills.

Doctor Who's gruelling production schedule produced up to 46 weeks of broadcast television a season and eventually proved too much for Hartnell, who was in the early stages of a debilitating form of arteriosclerosis.

When his Doctor returned to Doctor Who as a one-off guest-star in 1972, his health had noticeably deteriorated further and he died less than three years later.